Hybrid vehicle

ABSTRACT

A hybrid vehicle is provided that can be made to travel by means of motor generators (MG 1 , MG 2 ) while an engine (E) is stopped, the engine (E), which can reduce pumping loss by running with a cylinder in a cut-off state, being connected to a front wheel (Wf) via the first motor/generator (MG 1 ), an oil pump ( 13 ), a first clutch ( 14 ), a belt type continuously variable transmission (M), and a second clutch ( 20 ), and the second motor/generator (MG 2 ) being connected to a rear wheel (Wr). When the vehicle is made to travel by driving or braking the rear wheel (Wr) with the second motor/generator (MG 2 ), by driving the oil pump ( 13 ) with the first motor/generator (MG 1 ) in a state in which the engine (E), which has stopped running, is put into a cylinder cut-off state and the second clutch ( 20 ) is disengaged, a hydraulic pressure for shifting the belt type continuously variable transmission (M) is generated. It is thereby possible to generate a hydraulic pressure for shifting the belt type continuously variable transmission (M) while the engine (E) is stopped, without requiring a special electric oil pump.

FIELD OF THE INVENTION

The present invention relates to a hybrid vehicle in which an engineequipped with pumping loss reduction means is connected to a firstdriven wheel via a first motor/generator, an oil pump, a first clutch, ahydraulic automatic transmission, and a second clutch, and a secondmotor/generator is connected to a second driven wheel.

BACKGROUND ART

A hybrid vehicle in which a first motor/generator, an oil pump, a firstclutch, a belt type continuously variable transmission, a second clutch,and a second motor/generator are disposed between an engine and a drivenwheel is known from Japanese Patent Application Laid-open No.2001-200920. This conventional hybrid vehicle starts off and acceleratesby means of the driving force of the engine, and the driving force ofthe engine is assisted by making the first motor/generator function as amotor; during cruising, the engine is stopped, and the vehicle travelsby making the second motor/generator function as a motor; and duringdeceleration, electrical energy is recovered by making the first andsecond motor/generators function as generators.

When the engine is running, it is possible to generate a hydraulicpressure for shifting the belt type continuously variable transmissionwith the oil pump, which is driven by the engine, but when the engine isstopped and the vehicle travels by means of the driving force of thesecond motor/generator, since the oil pump generates no hydraulicpressure, when switching from traveling by means of the driving force ofthe second motor/generator to traveling by means of the driving force ofthe engine, there is a time lag until the oil pump generates a hydraulicpressure and shifting of the belt type continuously variabletransmission becomes possible, and there is a possibility that the ratiocontrol responsiveness might be degraded thus causing shift shock tooccur.

In the above-mentioned conventional arrangement, in addition to the oilpump driven by the engine, an electric oil pump is provided, and bygenerating a hydraulic pressure with the electric hydraulic pump whenthe engine is stopped, the actual ratio of the belt type continuouslyvariable transmission is rapidly made to coincide with a target ratiowhen switching over from traveling by means of the driving force of thesecond motor/generator to traveling by means of the driving force of theengine,.

However, in the above-mentioned conventional arrangement, since it isnecessary to employ an electric oil pump in addition to the oil pumpdriven by the engine, there is the problem that the number ofcomponents, cost, space, weight, etc. are increased by an amountcorresponding to the electric oil pump and a motor for driving it.

DISCLOSURE OF INVENTION

The present invention has been accomplished under the above-mentionedcircumstances, and it is an object thereof to provide a hybrid vehiclethat can travel by means of a motor/generator while an engine isstopped, and that enables hydraulic pressure for shifting an automatictransmission to be generated when the engine is stopped, withoutrequiring a special electric oil pump.

In order to attain this object, in accordance with a first aspect of thepresent invention, there is proposed a hybrid vehicle in which an engineequipped with pumping loss reduction means is connected to a firstdriven wheel via a first motor/generator, an oil pump, a first clutch, ahydraulic automatic transmission, and a second clutch, and a secondmotor/generator is connected to a second driven wheel, the second drivenwheel being different from the first driven wheel, characterized in thatwhen the vehicle is made to travel by driving or braking the seconddriven wheel with the second motor/generator, in order to shift theautomatic transmission a hydraulic pressure is generated by driving theoil pump with the first motor/generator in a state in which the pumpingloss of the engine, which has stopped running, is reduced by the pumpingloss reduction means and the second clutch is disengaged.

In accordance with this arrangement, when the vehicle is made to travelby driving or braking the second driven wheel with the secondmotor/generator while operation of the engine is stopped, since the oilpump is driven by the first motor/generator while the pumping loss ofthe engine is reduced by the pumping loss reduction means and the secondclutch is disengaged, not only is it possible to shift the automatictransmission with the hydraulic pressure generated by the existing oilpump without providing a special electric oil pump, but it is alsopossible to prevent shift shock from occurring by controlling the actualratio of the automatic transmission at a target ratio with goodresponsiveness when the engine is started and the first driven wheel isdriven via the automatic transmission. Moreover, since the enginerotated by the first motor/generator is in a state in which the pumpingloss is reduced, and the first motor/generator is disconnected from thefirst driven wheel by the second clutch being disengaged, not only is itpossible to minimize the power consumption of the first motor/generator,but it is also possible to start the engine rapidly by controlling theignition and starting the supply of fuel.

Furthermore, in accordance with a second aspect of the presentinvention, in addition to the first aspect, there is proposed the hybridvehicle wherein, when a deviation of the actual ratio of the automatictransmission from a target rate exceeds a predetermined value, theautomatic transmission is shifted while intermittently engaging thefirst clutch.

In accordance with this arrangement, since the automatic transmission isshifted by engaging the first clutch when the deviation of the actualratio from the target ratio exceeds the predetermined value, comparedwith a case in which shifting is carried out by continuously engagingthe first clutch it is possible to reduce the power consumption byminimizing the time for which the automatic transmission is driven bythe first motor/generator.

Moreover, in accordance with a third aspect of the present invention, inaddition to the first aspect, there is proposed the hybrid vehiclewherein, when the percentage change of a target ratio of the automatictransmission exceeds a predetermined value, the automatic transmissionis shifted while continuously engaging the first clutch.

In accordance with this arrangement, since the automatic transmission isshifted while continuously engaging the first clutch when the percentagechange of the target ratio of the automatic transmission exceeds thepredetermined value, shifting can be carried out without delay whenrapid shifting is necessary.

Furthermore, in accordance with a fourth aspect of the presentinvention, in addition to the first aspect, there is proposed the hybridvehicle wherein, when the remaining capacity of a battery connected tothe first and second motor/generators exceeds. a predetermined value,the required driving force of the vehicle is less than a predeterminedvalue, and the pumping loss of the engine can be reduced, traveling bymeans of the second motor/generator is permitted.

In accordance with this arrangement, since traveling by means of thesecond motor/generator is permitted when the remaining capacity of thebattery is sufficient, the remaining capacity of the battery does notbecome insufficient; since traveling by means of the secondmotor/generator is permitted when the required driving force of thevehicle is small, the driving force of the vehicle does not becomeinsufficient; and since traveling by means of the second motor/generatoris permitted when the pumping loss of the engine can be reduced, it ispossible to minimize the power consumption of the first motor/generatorfor driving the oil pump and the engine.

Moreover, in accordance with a fifth aspect of the present invention, inaddition to the fourth aspect, there is proposed the hybrid vehiclewherein, when the pumping loss reduction means is operated and travelingis carried out by means of the second motor/generator, a hydraulicpressure for shifting the automatic transmission is generated by drivingthe oil pump with the first motor/generator.

In accordance with this arrangement, since the hydraulic pressure forshifting the automatic transmission is generated by driving the oil pumpwith the first motor/generator when traveling is carried out by means ofthe second motor/generator in a state in which the pumping loss of theengine is reduced, it is possible to rapidly shift the automatictransmission in readiness for traveling by means of the engine whileminimizing the power consumption of the first motor/generator.

Furthermore, in accordance with a sixth aspect of the present invention,in addition to the first aspect, there is proposed the hybrid vehiclewherein, when a hydraulic pressure is generated in order to shift theautomatic transmission by driving the oil pump with the firstmotor/generator, the first clutch is disengaged.

In accordance with this arrangement, since the first clutch isdisengaged when the oil pump is driven by the first motor/generator, itis possible to prevent drag on the automatic transmission from thedriving force of the first motor/generator, thus reducing the powerconsumption.

A belt type continuously variable transmission M of an embodimentcorresponds to the automatic transmission of the present invention, afront motor/generator MG1 and a rear motor/generator MG2 of theembodiment correspond to the first motor/generator and the secondmotor/generator respectively of the present invention, and front wheelsWf and rear wheels Wr of the embodiment correspond to the first drivenwheel and the second driven wheel of the present invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 to FIG. 13 illustrate one embodiment of the present invention;

FIG. 1 is a diagram of the overall arrangement of a power transmissionsystem of a hybrid vehicle,

FIG. 2 is a flow chart of a drive mode determination routine,

FIG. 3 is a flow chart of a mode transition processing routine,

FIG. 4 is a flow chart of a stop mode processing routine,

FIG. 5 is a flow chart of an electric creep mode processing routine,

FIG. 6 is a flow chart of a deceleration mode processing routine,

FIG. 7 is a flow chart of an engine mode processing routine,

FIG. 8 is a flow chart of an electric mode processing routine,

FIG. 9 is a flow chart of a stop mode transition processing routine,

FIG. 10 is a flow chart of an electric creep mode transition processingroutine,

FIG. 11 is a flow chart of a deceleration mode transition processingroutine,

FIG. 12 is a flow chart of an engine mode transition processing routine,and

FIG. 13 is a flow chart of an electric mode transition processingroutine.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention is explained below with referenceto the attached drawings.

As shown in FIG. 1, connected in series to a crankshaft 11 of an engineE that can put all cylinders in a cut-off state are a frontmotor/generator MG1, a damper 12, an oil pump 13, a first clutch 14, andan input shaft 15 of a belt type continuously variable transmission M.An endless belt 19 is wound around a drive pulley 16 provided on theinput shaft 15 and a driven pulley 18 provided on a transmission outputshaft 17. The damper 12 has the functions of suppressing torque shockwhen a sudden torque is transmitted from the engine E and suppressingthe amplitude of torsional vibration of the crankshaft 11. Thetransmission output shaft 17 is connected to left and right front wheelsWf via a second clutch 20, a final drive gear 21, a final driven gear22, a front differential gear 23, and left and right axles 24. A rearmotor/generator MG2 is connected to left and right rear wheels Wr via arear differential gear 25 and left and right axles 26.

The front and rear motor/generatbrs MG1 and MG2 are connected to abattery 28 via a power drive unit 27.

During normal operation, an intake valve of the engine E is controlledso as to open and close in association with rotation of the crankshaft,but when running with the cylinders in a cut-off state, in order toreduce the pumping loss of the engine E, the intake valve is kept closedby pumping loss reduction means. Therefore, when the crankshaft 11 ofthe engine E is rotated by the front motor/generator MG1 while thecylinders of the engine E are in a cut-off state, the driving load canbe minimized.

Although not specifically illustrated in this embodiment, the engine E,the belt type continuously variable transmission M, the frontmotor/generator MG1, the rear motor/generator MG2, and the battery 28are controlled by corresponding ECUs (electronic control units), andthere is also provided an integrating ECU for integrating these ECUs.Control in the flow charts of FIG. 2 to FIG. 13 described below iscarried out by the integrating ECU.

With regard to the drive mode of a hybrid vehicle, there are five modes,that is, a ‘stop mode’, an ‘electric creep mode’, a ‘deceleration mode’,an ‘engine mode’, and an ‘electric mode’, and the mode is determined bythe flow chart of a drive mode determination routine of FIG. 2.

That is, if in step S1 a vehicle speed Vcar is 0 and a brake switch Brkis ON, then in step S2 it is determined that a requested drive modeDriveModeReq is the ‘stop mode’.

When the answer in step S1 is NO, then if in step S3 an acceleratorpedal degree of opening AP is fully closed, the brake switch Brk is OFF,the vehicle speed Vcar is less than a creep determination vehicle speedV_Crp, and a remaining battery capacity SOC exceeds a permitted electrictravel remaining capacity SOC_EV, then in step S4 it is determined thatthe requested drive mode DriveModeReq is the ‘electric creep mode’. The‘electric creep mode’ is a travel mode in which the vehicle is made tocreep by means of the driving force of the second motor/generator MG2.

When the answer in step S3 is NO, then if in step S5 the acceleratorpedal degree of opening AP is fully closed and the vehicle speed Vcarexceeds the creep determination vehicle speed V_Crp, or if in step S6the accelerator pedal degree of opening AP is fully closed, the brakeswitch Brk is ON, and the vehicle speed Vcar is not 0, then in step S7it is determined that the requested drive mode DriveModeReq is the‘deceleration mode’.

When the answers in steps S5 and S6 are both NO, if in step S8 arequired driving force F_REQ is not less than a permitted electrictravel driving force F_EV, or if in step S9 the remaining batterycapacity SOC does not exceed the permitted electric travel remainingcapacity SOC_EV, or if in step S10 a cylinder cut-off permission flagKYUOENR is not equal to 1 (cylinder cut-off permission), then in stepS11 it is determined that the requested drive mode DriveModeReq is the‘engine mode’. If the answers in steps S8 to S10 are all YES, then instep S12 it is determined that the requested drive mode DriveModeReq isthe ‘electric mode’. The ‘electric mode’ is a mode in which the vehicleis made to travel by the driving force of the second motor/generatorMG2.

Since traveling by means of the second motor/generator MG2 is permittedwhen the required driving force F_REQ is small in step S8, the drivingforce for the vehicle does not become insufficient. Since traveling bymeans of the second motor/generator MG2 is also permitted when theremaining capacity of the battery 28 is sufficient in step S9, thecapacity of the battery 28 does not become insufficient. Since travelingby means of the second motor/generator MG2 is also permitted when theengine E can be in a cylinder cut-off state in step S10, it is possibleto minimize the power consumption of the first motor/generator MG1,which rotates the engine E in a cylinder cut-off state together with theoil pump 13.

A mode transition processing routine is now explained with reference tothe flow chart of FIG. 3.

Firstly, in step S21, when a current drive mode DriveMode coincides withthe requested drive mode DriveModeReq, then if in step S22 the drivemode DriveMode is the ‘stop mode’, then in step S23 stop mode processingis carried out, if in step S24 the drive mode DriveMode is the ‘electriccreep mode’, then in step S25 electric creep mode processing is carriedout, if in step S26 the drive mode DriveMode is the ‘deceleration mode’,then in step S27 deceleration mode processing is carried out, if in stepS28 the drive mode DriveMode is the ‘engine mode’, then in step S29engine mode processing is carried out, and if in step S30 the drive modeDriveMode is the ‘electric mode’, then in step S31 electric modeprocessing is carried out.

On the other hand, when the current drive mode DriveMode does notcoincide with the requested drive mode DriveModeReq in step S21, if instep S32 the requested drive mode DriveModeReq is the ‘stop mode’, thenin step S33 stop mode transition processing is carried out, if in stepS34 the requested drive mode DriveModeReq is the ‘electric creep mode’,then in step S35 electric creep mode transition processing is carriedout, if in step S36 the requested drive mode DriveModeReq is the‘deceleration mode’, then in step S37 deceleration mode transitionprocessing is carried out, if in step S38 the requested drive modeDriveModeReq is the ‘engine mode’, then in step S39 engine modetransition processing is carried out, and if in step S40 the requesteddrive mode DriveModeReq is the ‘electric mode’, then in step S41electric mode transition processing is carried out.

A subroutine of the ‘stop mode processing’ of step S23 of the flow chartof FIG. 3 is now explained with reference to the flow chart of FIG. 4.

Firstly, in step S51 the first clutch 14 is disengaged, and in step S52the second clutch 20 is disengaged. In the subsequent step S53, when theremaining battery capacity SOC is not greater than a permitted idle stopcapacity SOC_IS (the remaining capacity that enables the engine E to berestarted even if it is put in an idle stop state), that is, when theremaining battery capacity SOC is insufficient, if in step S54 theengine E is firing fully, then in step S55 in order to carry outcharging with the front motor/generator MG1, a front motor/generatordrive command F_FrMot is set at an idle charge commandF_(—IdlChg (negative value), and in step S56 an engine drive command F)_ENGis set at the idle charge command F_IdlChg (positive value). By sodoing, while running the engine E the front motor/generator MG1 is madeto function as a generator, thus charging the battery 28.

In step S54, if the engine E is not firing fully, in step S57 the frontmotor/generator MG1 is made to function as a motor so as to crank theengine E, and in step S58 the engine drive command F_ENG is set at 0 (noload throttle degree of opening), thus starting the engine E.

A subroutine of the ‘electric creep mode processing’ of step S25 of theflow chart of FIG. 3 is now explained with reference to the flow chartof FIG. 5.

Firstly, in step S71 the second clutch 20 is disengaged, and in step S72driving the front motor/generator MG1 as a motor and idling the engine Ein a cylinder cut-off state allows the oil pump 13 to be driven whileminimizing the pumping loss of the engine E, thus generating a hydraulicpressure for shifting the belt type continuously variable transmissionM. In the subsequent step S73, the driving force command for the rearmotor/generator MG2 is set at a required driving force F_REQ, and therear motor/generator MG2 is made to function as a motor, thus making thevehicle creep electrically.

In the subsequent step S74, a target ratio RatioObj of the belt typecontinuously variable transmission M is calculated from the acceleratorpedal degree of opening AP and the vehicle speed Vcar, or the requireddriving force F_REQ and the vehicle speed Vcar. In step S75, when apercentage target ratio change |ΔRatioObj| exceeds a predeterminedvalue, that is, the percentage target ratio change |ΔRatioObj| is large,then in step S76 the first clutch 14 is engaged, and in step S77 shiftprocessing is carried out so that the actual ratio Ratio of the belttype continuously variable transmission M coincides with the targetratio RatioObj. The hydraulic pressure required in this process employsa hydraulic pressure that is generated by the oil pump 13 by driving theengine E in the cylinder cut-off state with the front motor/generatorMG1. In step S78, a ratio check timer TmRatioChk (down count timer) isset at a predetermined time TRATIOCHK.

As a result of the shift processing being carried out in step S77, instep S75 even if the percentage target ratio change |ΔRatioObj| does notexceed the predetermined value, if in the subsequent step S79 the ratiocheck timer TmRatioChk has timed up, then in step S80 the first clutch14 is engaged. If in step S81 a deviation |RatioObj−Ratio| of the actualratio Ratio from the target ratio RatioObj is not less than apredetermined value, that is, the deviation |RatioObj−Ratio| is large,then in step S82 shift processing is carried out so that the actualratio Ratio of the belt type continuously variable transmission Mcoincides with the target ratio RatioObj. The hydraulic pressurerequired in this process employs a hydraulic pressure that is generatedby the oil pump 13 by driving the engine E in the cylinder cut-off statewith the front motor/generator MG1. On the other hand, if in step S81the deviation |RatioObj−Ratio| is less than the predetermined value,then in step S78 the ratio check timer TmRatioChk is set at thepredetermined time TRATIOCHK. If in the step S79 the ratio check timerTmRatioChk has not timed up, then in step S83 the first clutch 14 isdisengaged.

In this way, if the percentage target ratio change |ΔRatioObj| exceedsthe predetermined value when the engine E is in the cylinder cut-offstate, then the first clutch 14 is engaged so as to drive the oil pump13, the actual ratio Ratio of the belt type continuously variabletransmission M is controlled at the target ratio RatioObj by thehydraulic pressure generated by the oil pump 13, each time thepredetermined time TRATIOCHK elapses the first clutch 14 is engaged todrive the oil pump 13, and in this process if the deviation|RatioObj−Ratio| of the actual ratio Ratio from the target ratioRatioObj is not less than the predetermined value, then the actual ratioRatio of the belt type continuously variable transmission M iscontrolled at the target ratio RatioObj, thereby enabling delay inresponse of shifting of the belt type continuously variable transmissionM to be prevented.

A subroutine of the ‘deceleration mode processing’ of step S27 of theflow chart of FIG. 3 is now explained with reference to the flow chartof FIG. 6.

The flow chart of FIG. 6 is substantially the same as that of FIG. 5;when the vehicle is decelerated, in the same manner as when the vehicleis made to creep electrically, the first clutch 14 is engaged underpredetermined conditions so as to rotate the drive pulley 16 and thedriven pulley 18 of the belt type continuously variable transmission M,and shifting to the target ratio RatioObj is carried out while checkingthe actual ratio Ratio; it is therefore possible to reliably prevent adelay in response of shifting of the belt type continuously variabletransmission M. The only difference is that, in step S73 of the flowchart of FIG. 5 the rear motor/generator driving force command F_RrMotis set at the required driving force F_REQ, and the rear motor/generatorMG2 is made to function as a motor so as to make the vehicle creepelectrically, but in step S73′ of the flow chart of FIG. 6 the rearmotor/generator driving force command F_RrMot is set at the requireddriving force F_REQ (regenerative braking), and the rear motor/generatorMG2 is made to function as a generator so as to generate a regenerativebraking force, thus recovering the kinetic energy of the vehicle aselectrical energy in the battery 28.

A subroutine of the ‘engine mode processing’ of step S29 of the flowchart of FIG. 3 is now explained with reference to the flow chart ofFIG. 7.

Firstly, in step S91 the first clutch 14 is engaged (including theso-called half-clutch control), in step S92 the second clutch 20 isengaged, and in step S93 the target ratio RatioObj of the belt typecontinuously variable transmission M is calculated from the acceleratorpedal degree of opening AP and the vehicle speed Vcar, or from therequired driving force F_REQ and the vehicle speed Vcar. In step S94,shift processing is carried out so that the actual ratio Ratio of thebelt type continuously variable transmission M coincides with the targetratio RatioObj.

In the subsequent step S95, if the mode is an assist mode, then in stepS96 the front motor/generator driving force command F_FrMot is set atthe front required assist driving force F_AstFrMot, the rearmotor/generator driving force command F_RrMot is set at the rearrequired assist driving force F_AstRrMot, and the front motor/generatorMG1 and the rear motor/generator MG2 are driven as motors, thusassisting the driving force of the engine E. In step S97, if the mode isa charging mode, in step S98 the front motor/generator driving forcecommand F_FrMot is set at a charging driving force F_Chg, the rearmotor/generator driving force command F_RrMot is set at 0, and the frontmotor/generator MG1 is driven as a generator, thus charging the battery28. In steps S95 and S97, if the mode is neither the assist mode or thecharging mode, in step S99 both the front motor/generator driving forcecommand F_FrMot and the rear motor/generator driving force commandF_RrMot are set at 0, thus running only the engine E.

In step S100, the driving force command F_ENG of the engine E iscalculated by subtracting, from the required driving force F_REQ, thefront motor/generator driving force command F_FrMot and the rearmotor/generator driving force command F_RrMot. That is, the totalrequired driving force of the engine E, the front motor/generator MG1,and the rear motor/generator MG2 is made to coincide with the requireddriving force F_REQ.

A subroutine of the ‘electric mode processing’ of step S31 of the flowchart of FIG. 3 is now explained with reference to the flow chart ofFIG. 8.

The flow chart of FIG. 8 is substantially the same as that of FIG. 5;when the vehicle travels electrically, in the same manner as when thevehicle creeps electrically, the first clutch 14 is engaged underpredetermined conditions so as to rotate the drive pulley 16 and thedriven pulley 18 of the belt type continuously variable transmission M,and shifting to the target ratio RatioObj is carried out while checkingthe actual ratio Ratio; it is therefore possible to reliably prevent adelay in response of shifting of the belt type continuously variabletransmission M. The only difference is that, in step S73 of the flowchart of FIG. 5 the required driving force F_REQ of the rearmotor/generator MG2 is a small value for electric creep traveling, butin step S73″ of the flow chart of FIG. 8, the required driving forceF_REQ of the rear motor/generator MG2 is a large value for electricaltraveling.

The subroutine of the ‘stop mode transition processing’ of step S33 ofthe flow chart of FIG. 3 is explained with reference to the flow chartof FIG. 9.

Firstly, in step S111 the first clutch 14 is engaged, in step S112 thesecond clutch 20 is disengaged, and in step S113 the target ratioRatioObj of the belt type continuously variable transmission M iscalculated from the accelerator pedal degree of opening AP and thevehicle speed Vcar, or the required driving force F_REQ and the vehiclespeed Vcar. If in step S114 the deviation |RatioObj−Ratio| of the actualratio Ratio from the target ratio RatioObj is not less than apredetermined value, that is, the deviation |RatioObj−Ratio| is large,then in step S115 shift processing is carried out so that the actualratio Ratio of the belt type continuously variable transmission Mcoincides with the target ratio RatioObj. On the other hand, if in stepS114 the deviation |RatioObj−Ratio| is less than the predeterminedvalue, then the drive mode DriveMode is set at the stop mode Stop. Inthis way, in a state in which the second clutch 20 is disengaged and thefirst clutch 14 is engaged, after the actual ratio Ratio of the belttype continuously variable transmission M is made to coincide with thetarget RatioObj, a transition to the ‘stop mode’ is carried out.

A subroutine of the ‘electric creep mode transition processing’ of stepS35 of the flow chart of FIG. 3 is explained with reference to the flowchart of FIG. 10.

Firstly, in step S121 the first clutch 14 is disengaged, in step S112the second clutch 20 is disengaged, and in step S123 the frontmotor/generator MG1 is driven as a motor so as to make the engine E idlein a cylinder cut-off state, thereby generating a hydraulic pressure forshifting the belt type continuously variable transmission M by drivingthe oil pump 13 while minimizing the pumping loss of the engine E. If inthe subsequent step S124 the engine rotational speed Ne exceeds acylinder cut-off lower rotational speed limit, or if the hydraulicpressure generated by the oil pump 13 exceeds a cylinder cut-off lowerhydraulic pressure limit, then in step S125 the drive mode DriveMode isset at the electric creep mode EVCeep.

A subroutine of the ‘deceleration mode transition processing’ of stepS37 of the flow chart of FIG. 3 is explained with reference to the flowchart of FIG. 11.

In step S131 the drive mode DriveMode is set at the deceleration modeDec.

A subroutine of the ‘engine mode transition processing’ of step S39 ofthe flow chart of FIG. 3 is explained with reference to the flow chartof FIG. 12.

Firstly in step S141 the first clutch 14 is engaged, then in step S142 acylinder cut-off solenoid is turned OFF so as to cancel the cylindercut-off state of the engine E, a fuel injection permission INJ is turnedON, and an ignition permission IG is turned ON. In the subsequent stepS143, the target ratio RatioObj of the belt type continuously variabletransmission M is calculated from the accelerator pedal degree ofopening AP and the vehicle speed Vcar, or from the required drivingforce F_REQ and the vehicle speed Vcar, and in step S144 a target enginerotational speed NeCmd is calculated from the target ratio RatioObj andthe vehicle speed Vcar. Subsequently, in step S145 shift processing iscarried out so that the actual ratio Ratio of the belt type continuouslyvariable transmission M coincides with the target ratio RatioObj, and instep S146 the front motor/generator MG1 is operated as a motor or agenerator so that the engine rotational speed Ne coincides with thetarget engine rotational speed NeCmd.

If in the subsequent step S147 the deviation |RatioObj−Ratio| of theactual ratio Ratio from the target ratio RatioObj is not less than apredetermined value, that is, if the deviation |RatioObj−Ratio| islarge, or if in step S148 the percentage target ratio change |ΔRatioObj|is not less than a predetermined value, that is, the percentage targetratio change |ΔRatioObj| is large, or if in step S149 the engine E isnot firing fully, or if in step S150 if the deviation |NeCmd−Ne| of theengine rotational speed Ne from the target engine rotational speed NeCmdis not less than a predetermined value, that is, the deviation|NeCmd−Ne| is large, then in step S151 the second clutch 20 isdisengaged, in step S152 the rear motor/generator driving force commandF_RrMot is set at the required driving force F_REQ, and in step S153 theengine driving force command F_ENG is set at 0.

Here, a throttle valve should be opened by an amount corresponding to ano-load state of the engine E, which depends on the engine rotationalspeed Ne. The purpose of the throttle valve being opened by the amountcorresponding to the no-load state is to make the output torque of thecrankshaft 11 equal to 0, that is, the engine E is made to carry outwork corresponding to its friction. In this way, the rearmotor/generator MG2 is made to generate a driving force until the targetratio RatioObj and the target engine rotational speed NeCmd areachieved.

If the answers in steps S147 to S150 are all YES, that is, if travelingby means of the engine E is possible, then in step S154 the secondclutch 20 is engaged (including the so-called half-clutch), and in stepS155 the engine driving force command F_ENG is set at the requireddriving force F_REQ. In the subsequent step S156 the actual enginedriving force F_ENG_ACT is calculated from the engine rotational speedNe and an intake negative pressure Pb (or an intake air volume), and instep S157 the rear motor/generator driving force command F_RrMot is setat the required driving force F_REQ—the actual engine driving forceF_ENG_ACT. If in the subsequent step S158 the actual engine drivingforce F_ENG_ACT coincides with the required driving force F_REQ, thatis, the rear motor/generator MG2 stops and only the engine E generates adriving force, then in step S159 the drive mode DriveMode is set at theengine mode ENG.

A subroutine of the ‘electric mode transition processing’ of step S41 ofthe flow chart of FIG. 3 is now explained with reference to the flowchart of FIG. 13.

Firstly in step S161 the first clutch 14 is engaged, in step S162 thesecond clutch 20 is engaged, then in step S163 the cylinder cut-offsolenoid is turned OFF so as to cancel the cylinder cut-off state of theengine E, the fuel injection permission INJ is turned ON, and theignition permission IG is turned ON. In the subsequent step S164, thetarget ratio RatioObj of the belt type continuously variabletransmission M is calculated from the accelerator pedal degree ofopening AP and the vehicle speed Vcar, or the required driving forceF_REQ and the vehicle speed Vcar, in step S165 shift processing iscarried out so that the actual ratio Ratio of the belt type continuouslyvariable transmission M coincides with the target ratio RatioObj, and instep S166 the engine driving force command F_REQ is set at 0 (no-loadthrottle degree of opening).

In the subsequent step S167, the actual engine driving force F_ENG_ACTis calculated from the engine rotational speed Ne and the intakenegative pressure Pb (or an intake air volume), and in step S168 therear motor/generator driving force command F_RrMot is set at therequired driving force F_REQ—the actual engine driving force F_ENG_ACT.In the subsequent step S169 if the actual engine driving force F_ENG_ACTis 0, that is, the rear motor/generator MG2 generates all of therequired driving force F_REQ, then in step S170 the drive mode DriveModeis set at the electric mode EV.

As hereinbefore described, in accordance with the present embodiment,when the vehicle travels while the operation of the engine E is stoppedand the rear wheels Wr are driven or braked by the rear motor/generatorMG2, that is, in the ‘electric creep mode’ of FIG. 5, the ‘decelerationmode’ of FIG. 6, and the ‘electric mode’ of FIG. 8, the oil pump 13 isdriven by the front motor/generator MG1 in a state in which the pumpingloss of the engine E is reduced by the pumping loss reduction meansmaintaining the intake valve of the engine E in a valve closed state andthe second clutch 20 is disengaged. It is therefore possible to shiftthe belt type continuously variable transmission M by means of thehydraulic pressure generated by the oil pump 13 even when the engine Eis stopped, and it is possible to prevent shift shock from occurring bycontrolling the actual ratio of the belt type continuously variabletransmission M at a target ratio with good responsiveness when theengine is started and the front wheels Wf are driven via the belt typecontinuously variable transmission M.

Here, since the engine E rotated by the front motor/generator MG1 is ina state in which the pumping loss is reduced, and the frontmotor/generator MG1 is disconnected from the front wheels Wf by thesecond clutch 20 being disengaged, it is possible to minimize the powerconsumption by reducing the load of the front motor/generator MG1.Furthermore, by disengaging the first clutch 14 when the frontmotor/generator MG1 is driven, it is possible to prevent drag on thebelt type continuously variable transmission M, thus reducing the powerconsumption of the front motor/generator MG1. Moreover, since the engineE is made to idle by the front motor/generator MG1, the engine E can bestarted rapidly by controlling the ignition and starting to supply fuel,and it is possible to smoothly and rapidly transfer from a state oftraveling by means of the rear motor/generator MG2 to a state oftraveling by means of the engine E.

Furthermore, when the vehicle travels by means of the rearmotor/generator MG2 while the engine E is stopped, since the belt typecontinuously variable transmission M is shifted by intermittentlyengaging the first clutch 14 when the deviation |RatioObj−Ratio| of theactual ratio from the target ratio of the belt type continuouslyvariable transmission M exceeds a predetermined value, compared with acase in which shifting is carried out by continuously engaging the firstclutch 14 while the engine E is stopped, it is possible to reduce thepower consumption by minimizing the time for which the belt typecontinuously variable transmission M is driven by the frontmotor/generator MG1. Moreover, since shifting is carried out bycontinuously engaging the first clutch 14 when the percentage targetratio change |ΔRatioObj| of the belt type continuously variabletransmission M exceeds a predetermined value, when it is necessary torapidly shift the belt type continuously variable transmission M, it canbe shifted without delay.

Although an embodiment of the present invention is explained above, thepresent invention can be modified in a variety of ways without departingfrom the scope and spirit thereof.

For example, in the embodiment, the belt type continuously variabletransmission M is illustrated as the automatic transmission, but thepresent invention can also be applied to a continuously variabletransmission other than the belt type continuously variable transmissionor to a stepped automatic transmission.

Furthermore, instead of the damper 12, a torque converter may beprovided.

Moreover, the pumping loss reduction means is not limited to theembodiment, and may employ means in which both an intake valve and anexhaust valve are fully closed, or a throttle valve is fully opened.

Furthermore, with regard to the drive mode of the vehicle V, other thanthose described in the embodiment, there can be considered a mode inwhich the driving force of the engine E is assisted by one or both ofthe first and second motor/generators MG1 and MG2, or a mode in which,without using the engine E, the vehicle travels by means of the drivingforce of both of the first and second motor/generators MG1 and MG2.

1. A hybrid vehicle in which an engine (E) equipped with pumping lossreduction means is connected to a first driven wheel via a firstmotor/generator (MG1), an oil pump (13), a first clutch (14), ahydraulic automatic transmission (M), and a second clutch (20), and asecond motor/generator (MG2) is connected to a second driven wheel (Wr),the second driven wheel (Wr) being different from the first driven wheel(Wf), characterized in that when the vehicle is made to travel bydriving or braking the second driven wheel (Wr) with the secondmotor/generator (MG2), in order to shift the automatic transmission (M)a hydraulic pressure is generated by driving the oil pump (13) with thefirst motor/generator (MG1) in a state in which the pumping loss of theengine (E), which has stopped running, is reduced by the pumping lossreduction means and the second clutch (20) is disengaged.
 2. The hybridvehicle according to claim 1 wherein, when a deviation of the actualratio of the automatic transmission (M) from a target ratio exceeds apredetermined value, the automatic transmission (M) is shifted whileintermittently engaging the first clutch (14).
 3. The hybrid vehicleaccording to claim 1 wherein, when the percentage change of a targetratio of the automatic transmission (M) exceeds a predetermined value,the automatic transmission (M) is shifted while continuously engagingthe first clutch (14).
 4. The hybrid vehicle according to claim 1wherein, when the remaining capacity of a battery (28) connected to thefirst and second motor/generators (MG1, MG2) exceeds a predeterminedvalue, the required driving force of the vehicle is less than apredetermined value, and the pumping loss of the engine (E) can bereduced, traveling by means of the second motor/generator (MG2) ispermitted.
 5. The hybrid vehicle according to claim 4 wherein, when thepumping loss reduction means is operated and traveling is carried out bymeans of the second motor/generator (MG2), a hydraulic pressure forshifting the automatic transmission (M) is generated by driving the oilpump (13) with the first motor/generator (MG1).
 6. The hybrid vehicleaccording to claim 1 wherein, when a hydraulic pressure is generated inorder to shift the automatic transmission (M) by driving the oil pump(13) with the first motor/generator (MG1), the first clutch (14) isdisengaged.